I liked the idea to have an oscilloscope in my home. I used an USB audio adapter as input device and a computer with a software application as display. This device can measure signals only in the audio spectrum, which is a big limitation in performance. However, this can be enough at home for many hobby applications. Also this device can measure signals with amplitude below 5V. This article is about the first prototype I made. Based on this experience, I started later another project, more complex [see link 1]. For both projects, I used the same software application. Details are in my second project.

The USB adapter I used (connected to a computer with Windows 7) is recognized by the operating system and a driver is installed automatically at first connection. Usually we need to install a driver provided by the manufacturer of the USB module/chipset before connecting the device to the computer. Bellow are some images with modifications I made to this module.

- I removed the audio connectors to make space for new components
- two electrolytic capacitors from output were removed for the same reason as above
- one resistor and one capacitor were also removed (see the arrows in figure 2)
- in place of above mentioned capacitor I made a strap (connection) as you can see in figure 2 (upper arrow).
- additional components were added (according to figures 3 and 5)
- homemade probe was added. The cable was soldered directly to USB module printed circuit board (PCB)

The components added at the input of module function as voltage attenuator (R1 and R2), overvoltage protection (R1, R3, D1 and D2) and AC component separation (C1). Because of C1, we can measure only AC signals. As we have mentioned above, we have built later a different hardware to add more features compared to this one. More details about software, calibration, instructions for use, links and additional information (some applicable also for this oscilloscope) can be found on next article [1].

Warning: This oscilloscope provides no galvanic isolation between its inputs/outputs and USB interface. In other words, there is no electric isolation between you and devices you measure (including the computer where this oscilloscope is connected). Therefore, you have to pay attention for the voltages that exist in your working environment. In some circumstances, this can cause injuries to users or damage to the oscilloscope, computer or other devices. In addition to observe all the applicable safety regulations, a good idea is to check first with a multimeter the AC and DC voltages between all the electric and electronic devices that you use in your activity.

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Links:
[1] - A more complex oscilloscope: Oscilloscope with USB audio adapter 2